Reflection characteristic measuring apparatus

ABSTRACT

A measuring apparatus includes an illumination device including a surface light source, a detector configured to detect a light intensity distribution formed on a light-receiving surface by reflected light, and a processor configured to obtain the reflection characteristic based on first data of the light intensity distribution detected by the detector. The processor is configured to estimate, based on the first data, second data of a light intensity distribution formed by specular reflected light and third data of a light intensity distribution formed by diffuse reflected light in a case where a point light source is disposed at each position in a light-emitting region of the surface light source, and to estimate, based on the second data and the third data, a light intensity distribution formed by reflected light from the surface.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a measuring apparatus for measuring areflection characteristic of a surface.

Description of the Related Art

Conventionally, it is an important proposition to evaluate a printedproduct, a painted surface, and an exterior of a product, and JIS andISO set standards for measuring a reflection characteristic of an objectsurface (surface) such as gloss. For example, as standards for measuringa specular gloss, JIS Z 8741 and the like are set. As standards formeasuring a haze which represents a degree of image unclearness(dullness of a sample surface), ISO13803, ASTM E 430, and the like areset. As standards for measuring distinctness-of-image gloss associatedwith gloss, ASTM E 430, ASTM D 5767, and the like are set. As standardsfor measuring an image clarity (image clearness), JIS K 7374, JIS H8686, and the like are set.

In respective standards, since there are surfaces suitable andunsuitable for measurement, the user has to select an optimal standardfrom the aforementioned standards depending on the situation, so as tomeasure the reflection characteristic. FIG. 6 shows a specular glossmeasuring method defined in JIS Z 8741. A light beam from a light source1 is roughly condensed by a lens 2 to be condensed on a rectangularlight source slit 31, which is set to have an aperture angle defined bythe standard, and the light source slit 31 forms a secondary lightsource having the defined aperture angle. A light beam from the lightsource slit 31 is converted into a nearly parallel light beam by a lens41, and a surface 10 is irradiated with the nearly parallel light beam.Light reflected by the surface 10 has a unique reflection patterndepending on a state of the surface 10, and is condensed again by a lens42, thus forming an image of the light source slit 31 on alight-receiving slit 32. Light, which has passed through thelight-receiving slit 32, enters a light-receiving element 100, and isoutput as a photoelectric signal from the light-receiving element 100. Aspecular gloss measuring apparatus shown in FIG. 6 calculates aglossiness of the surface 10 using a relative intensity between theamount of light reflected by the surface 10 and an amount of lightreflected by a reference surface, which amount is measured in advance.The specular gloss measuring apparatus shown in FIG. 6 can definebrightness of reflection of a light source, but does not define ablurred degree of reflection of a light source, and cannot perfectlyexpress the state of the surface 10.

FIG. 7 shows the arrangement of an apparatus for measuring a hazedefined by ASTM E 430. A light beam from a light source 1 is roughlycondensed by a lens 2 to be condensed on a light source slit 31, whichis set to have an aperture angle defined by the standard, and the lightsource slit 31 forms a secondary light source having the definedaperture angle. A light beam from the light source slit 31 is convertedinto a nearly parallel light beam by a lens 41, and a surface 10 isirradiated with the nearly parallel light beam. Light reflected by thesurface 10 has a unique reflection pattern depending on a state of thesurface 10, and is condensed again by a lens 42, thus forming an imageof the light source slit 31 on a light-receiving slit 33. Light, whichhas passed through the light-receiving slit 33, enters a light-receivingelement, and is output as a photoelectric signal. The light-receivingslit 33 includes three slits 33 a, 33 b, and 33 c, which are set at18.1°, 20°, and 21.9° with respect to a perpendicular to the surface 10.The slit 33 b is used to measure a specular gloss, and the slits 33 aand 33 c are used to measure a haze. The haze is an index indicating adegree of image unclearness. However, since an angle difference fromspecular reflected light of the slits 33 a and 33 c is small, a state ofthe surface 10 suitable for measurement of a haze is limited. When areflection image exhibits unclearness beyond recognition, it isdifficult to calculate a haze from the measurement result of themeasuring apparatus shown in FIG. 7.

A distinctness-of-image gloss is measured using an apparatus having thesame arrangement as that shown in FIG. 7 except for dimensions of theslits and a value calculation formula. More specifically, angles of theslits 33 a, 33 b, and 33 c with respect to the perpendicular to thesurface 10 are 19.7°, 20°, and 20.3°, and slit sizes are different. Likein measurement of a haze and the like, it is difficult for the surface10 whose reflection image exhibits unclearness beyond recognition tocalculate a distinctness-of-image gloss.

FIG. 8 shows the arrangement of an apparatus used in an image claritytest method defined by JIS K 7374. A light beam from a light source 1passes through a slit 31 and enters a lens 41 to be converted intoparallel light, with which a surface 10 is irradiated. Reflected lightby the surface 10 has a unique reflection pattern depending on a stateof the surface 10, and is condensed again by a lens 42, thus forming animage of the light source slit 31 on a comb-tooth slit 50. Thecomb-tooth slit 50 is configured by five types of slits having differentpitches. Contrast values are acquired by calculating maximum and minimumtransmitted light amounts upon moving the comb-tooth slit 50 in a slitarray direction, thus expressing the state of the surface 10 by fivecontrast values. Since the image clarity measuring method evaluates theclearness of a reflection image using contrast values, the brightness ofthe reflection image cannot be discussed.

Japanese Patent Laid-Open No. 2008-256454 describes an apparatus andmethod for measuring a specular gloss of a surface, and Japanese PatentLaid-Open No. 2007-24655 describes an apparatus and method for measuringan image clarity of a surface.

As described above, the measuring apparatuses defined by the respectivestandards have respective features, and measure different targetreflection characteristics of a surface. Also, Japanese Patent Laid-OpenNos. 2008-256454 and 2007-24655 disclose the apparatuses and methods formeasuring reflection characteristics of a surface. However, theseapparatuses and methods can only measure limited reflectioncharacteristics of the surface. Therefore, the user in need of variousreflection characteristics of a surface, has to prepare for measuringapparatuses of a plurality of methods, and has to selectively use themdepending on the situation. For this reason, the user requires cost forpurchasing a plurality of apparatuses, and a place for housing theplurality of apparatuses, thus imposing a load on the user.

SUMMARY OF THE INVENTION

The present invention provides, for example, a technique which enables asingle measuring apparatus to measure a plurality of types of reflectioncharacteristics of a surface.

The present invention provides a measuring apparatus for measuring areflection characteristic of a surface, the measuring apparatuscomprising: an illumination device including a surface light source andconfigured to illuminate the surface with light from the surface lightsource; a detector configured to detect a light intensity distributionformed on a light-receiving surface by reflected light from the surfaceilluminated by the illumination device; and a processor configured toobtain the reflection characteristic based on first data of the lightintensity distribution detected by the detector, wherein the processoris configured to estimate, based on the first data, second data of alight intensity distribution formed on the light-receiving surface byspecular reflected light from the surface and third data of a lightintensity distribution formed on the light-receiving surface by diffusereflected light from the surface in a case where a point light source isdisposed at each position in a light-emitting region of the surfacelight source, and to estimate, based on the second data and the thirddata, a light intensity distribution formed on the light-receivingsurface by reflected light from the surface in a case where a lightsource, at least one of a shape and a size of a light-emitting region ofwhich is different from that of the surface light source, is disposed inplace of the surface light source.

Further features of the present invention will become apparent from thefollowing description of embodiments with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the arrangement of a measuringapparatus according to the first embodiment;

FIG. 2 is a graph showing an intensity distribution when specularreflected light and diffuse reflected light are combined;

FIG. 3 shows graphs of a transition of intensity distributions ofspecular reflected light in case of a circular aperture, and that ofintensity distributions of specular reflected light in case of a pointlight source;

FIG. 4 is a schematic view showing the arrangement of a measuringapparatus according to the second embodiment;

FIG. 5 is a schematic view showing the arrangement of a measuringapparatus according to the third embodiment;

FIG. 6 is a view showing the arrangement of a specular gloss measuringapparatus designated by JIS Z 8741;

FIG. 7 is a view showing the arrangement of a haze measuring apparatusdesignated by ASTM E 430; and

FIG. 8 is a view showing the arrangement of an image clarity measuringapparatus designated by JIS K 7374.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detailhereinafter with reference to the accompanying drawings.

First Embodiment

FIG. 1 shows a schematic arrangement of a measuring apparatus formeasuring a reflection characteristic of a surface according to thefirst embodiment. An illumination device from a light source 1 to a lens41 and a light-receiving device from a lens 42 to a two-dimensionallight-receiving element (detector) 100 are disposed to respectively haveangles θ and θ′ with respect to a perpendicular to a surface 10. Theincident angle θ and reflection angle θ′ are set for each standard to becompliant with that standard which defines a reflection characteristicof the surface 10. When a reflection characteristic is a specular gloss,the incident angle θ and light-receiving angle θ′ are set at any of 20°,45°, 60°, and 85°. When a reflection characteristic is a haze, theincident angle θ and reflection angle θ′ are set at 20°. When areflection characteristic is an image clarity, the incident angle θ andreflection angle θ′ are set at any of 45° and 60°. When a reflectioncharacteristic is a distinctness-of-image gloss, the incident angle θand reflection angle θ′ are set at 20°.

A light beam emitted from the light source 1 is condensed on a stop 31having a circular aperture of φ1 mm by a lens 2. On the stop 31, animage of the light source 1 is temporarily formed as a circularsecondary light source (surface light source) of φ1 mm. A light beamemitted from the stop 31 becomes a diverging light beam again, and isconverted into parallel light by the lens 41, thus illuminating thesurface 10. Reflected light from the surface 10 has a unique reflectionpattern depending on the reflection characteristic of the surface 10,and is received by a light-receiving surface of the two-dimensionallight-receiving element 100. The two-dimensional light-receiving element100 detects an intensity distribution of light formed on thelight-receiving surface by the reflected light form the surface 10, andoutputs first data to a processor 110. More specifically, the first datais a reflection pattern like a BRDF 1 with which an intensity changesaccording to an angle. Note that the BRDF (Bidirectional ReflectanceDistribution Function) is a function which expresses a reflectancedistribution of the surface 10, and represents a ratio of reflectedlight luminance to incident light illuminance. More strictly, a BRDF ata certain point on an object surface depends on two directions, that is,incident and reflection directions, and is defined as a ratio of anintensity of reflected light in an observation direction to that ofincident light from an illumination direction. A signal received by thetwo-dimensional light-receiving element 100 can express a reflectioncharacteristic unique to the surface 10 by trimming an output along anAA section on the two-dimensional light-receiving element 100.

The intensity distribution of reflected light received by thetwo-dimensional light-receiving element 100 is trimmed along the AAsection to cope with calculations of the respective standards whichdefine the reflection characteristics. When the intensity distributionof reflected light is trimmed along another section in addition to theAA section, an anisotropy of the reflection characteristic of thesurface 10 can also be measured. The reflection pattern BRDF 1 receivedby the two-dimensional light-receiving element 100 is obtained bycombining a BRDF 1A by specular reflected light and a BRDF 1B by diffusereflected light, as shown in FIG. 2. The specular reflected light isalso called surface reflected light, and the diffuse reflected light isalso called scattered light. Since the BRDF 1B by diffuse reflectedlight corresponds to so-called a background color and brightness of thesurface 10, and seems to have equal brightness independently of a visualline angle, the brightness is expressed by a model which is proportionalto COS θ with respect to a visual line angle θ, and is called Lambertscattering. The BRDF 1A by specular reflected light corresponds to astate of reflection of the light source 1, is normally modeled by aGaussian distribution, and is defined by a spread degree and intensityof the distribution as parameters.

In this case, attention will be focused on the BRDF 1A based on thespecular reflected light obtained by the two-dimensional light-receivingelement 100 using the stop 31 having the circular aperture. The lightintensity distribution BRDF 1A by specular reflected light when thecircular aperture is used changes from a BRDF 1Aa to a BRDF 1Ad duringprocesses in which the surface 10 transits from a specular surface to ascattering surface, as shown in FIG. 3. When the surface 10 is aspecular surface, since the circular aperture of the stop 31 isprojected intact on the two-dimensional light-receiving element 100, arectangular BRDF 1Aa with a sharp edge is output. During processes inwhich the surface 10 becomes closer to a diffusing surface, therectangular shape is broken, and a nearly Gaussian distribution like aBRDF 1Ad is finally output.

Assume that four surfaces 10 which exhibit reflection patterns of BRDFs1Aa to 1Ad by specular reflected light when the surface 10 is irradiatedwith light using the stop 31 having the circular aperture will berespectively referred to as surfaces 10 a to 10 d. Assume that BRDFs 2by specular reflected light obtained by the two-dimensionallight-receiving element 100 when a point light source (for example, alight source of φ10 μm) is disposed at one of a plurality of positionsin a plane of the stop 31 and the surfaces 10 a to 10 d are illuminatedwith light coming from that light source will be respectively referredto as BRDFs 2 a to 2 d. The BRDFs 2 a to 2 d are simple Gaussiandistribution patterns in which only a spread degree and intensity arechanged during transition processes from specular surfaces to scatteringsurfaces of the surfaces 10 a to 10 d. The BRDFs 2 a to 2 d can beestimated from addition calculations under the assumption that thecircular aperture of the stop 31 is a set of point light sources.Alternatively, the BRDFs 2 a to 2 d can be calculated via actualmeasurements by arranging a point light source at each of the pluralityof positions in the plane of the stop 31. In the first embodiment,information indicating the relationship between the BRDFs 1Aa to 1Ad andthe BRDFs 2 a to 2 d is acquired in advance by calculations or actualmeasurements, and is stored in a memory 120 of the measuring apparatus.

When the BRDFs 2 a to 2 d are to be calculated, for example, a size φ ofa point light source is set to fall within a range of several 1 μm toseveral ten 1 μm, and a blurred pattern on the two-dimensionallight-receiving element 100 is modeled by being approximated to aGaussian distribution. Assuming that the circular aperture of the stop31 is a set of point light sources, a blurred image of the circularaperture on the two-dimensional light-receiving element 100 can beassumed to be a set of blurred images of the point light sources. Sumtotals of light intensities obtained from the respective point lightsources as many as the numbers of point light sources on a planecoordinate system on the two-dimensional light-receiving element 100 areequal to the BRDFs 1Aa to 1Ad. Based on the aforementioned principle,the BRDFs 2 a to 2 d can be calculated (back-calculated) from actuallymeasured values of the BRDFs 1Aa to 1Ad.

The BRDF 1A by specular reflected light when the stop 31 having thecircular aperture is used and the reflection pattern BRDF 2 of a pointlight source can be associated with each other using, for example, ahalf width and peak ratio of the reflection pattern. Also, since thehalf width of the reflection pattern is not monotonically increased nearspecular reflection during blurring processes of an image, the BRDF 1Amay be associated with the BRDF 2 using a width other than the halfwidth, for example, a ⅓ width of a peak. The width of the peak used inassociation with the BRDF 2 may be other widths such as a ¼ width inaddition to the ⅓ width. However, when the width of the peak used inassociation with the BRDF 2 falls below a ⅕ width, a boundary betweenspecular reflected light and diffuse reflected light (scattered light)becomes unspecific, and an inclination of a Gaussian distributionwaveform becomes moderate, thus readily causing errors. Alternatively, acorrelation of maximum values (peaks of differential waveforms) ofinclination values of profiles of the BRDFs 2 a to 2 d and BRDFs 1Aa to1Ad or that of distances between maximum values of inclinations ofprofiles may be calculated, or a correlation may be calculated bycombining them. With the aforementioned method, the processor 110 cancalculate the reflection pattern BRDF 2 of the point light source fromthe BRDF 1A.

For example, assume that a pinhole of φ10 μm is actually disposed as apoint light source at a position of the circular aperture of the stop31. Then, the obtained light amount is only about 1/10000 of thatobtained when the stop 31 having the circular aperture is used. For thisreason, it becomes difficult to precisely measure reflection profiles,or an accumulation time of the two-dimensional light-receiving element100 has to be prolonged, resulting in a low throughput. Therefore, it isvery effective to dispose the stop 31 having the circular aperture of φ1mm or more, and to calculate the reflection pattern BRDF 2 of the pointlight source by calculations in terms of signal quality. In the firstembodiment, the processor 110 divides the BRDF 1 into the BRDF 1A byspecular reflected light and the BRDF 1B by diffuse reflected light, andthen calculates a correlation between the BRDF 1A and the reflectionpattern BRDF 2 by specular reflected light of the point light source.

However, the processor 110 may estimate, based on the BRDF 1, data ofthe light intensity distribution formed on the light-receiving surfaceby reflected light when a point light source is disposed at one of aplurality of positions of the circular aperture of the stop 31. Theprocessor 110 can calculate the BRDF 2 (second data) by specularreflected light and a BRDF 3 (third data) by diffuse reflected light bydividing the estimated data. In this case, the processor 110 cancalculate the BRDF 3 based on the BRDF 1B by diffuse reflected light anda ratio between the size of the point light source and the circularaperture of the stop 31.

The BRDF 1B by diffuse reflected light will be described below. As isknown, diffuse reflected light can be modeled by being approximated toLambert scattering. The Lambert scattering defines that a reflectedlight amount ratio to an angle θ is COS θ based on the fact that thebrightness of object on a perfectly diffusing surface (perfect diffusesurface or Lambertian surface) is constant independently of a visualline. When a BRDF based on reflected light generated by a referencesurface having a given diffuse reflectance (diffuse reflectedlight/incident light) is measured in advance using this measuringapparatus, the BRDF 3 based on the BRDF 1B by diffuse reflected lightcan be estimated by giving parameters of the diffuse reflectance. Sincelevels of specular reflected light and diffuse reflected light to bemixed are determined by an area of the light source 1, the diffusereflectance and the area of the light source 1 can be used incalculations to be described later when they are stored in the memory120.

A process for calculating standard values of various reflectioncharacteristics defined by arbitrary measuring conditions from thereflection pattern BRDF 2 of the point light source derived in the aboveprocesses will be described below. A measuring condition of a settablereflection characteristic includes a shape and size of an arbitrarylight source, an arbitrary evaluation region on the light-receivingsurface, an incident angle of parallel light, and the like.

For example, assume that a glossimeter described in JIS Z 8741 of aspecular gloss is configured. The processor 110 calculated the BRDF 2 byspecular reflected light in case of φ10 μm in the above processes. Whena specular gloss is to be measured at an incident angle of 20°, anaperture on the light source side is a rectangle having a width of 0.75°and a length of 2.5°, which are defined by an aperture angle. Using afocal length F of the lens 41 and an aperture angle β, a size of theaperture on the light source side can be calculated by F×COS β.Therefore, if the focal length is 50 mm, it can be calculated that arectangular slit having a width of 0.65 mm and a length of 2.18 mm isrequired as the aperture on the light source side.

A reflection pattern by specular reflected light on the two-dimensionallight-receiving element 100 when this rectangular slit is used can becalculated by the processor 110 by adding light amounts on atwo-dimensional space to have the rectangular slit of the width of 0.65mm and the length of 2.18 mm as a set of point light sources of φ10 μm.The light intensity distribution by diffuse reflected light when thisrectangular slit is used can be calculated by multiplying the dividedBRDF 1B by an area ratio 0.65×2.18÷(π×0.5²)=1.8 of the rectangular slitwith respect to the circular aperture. In this manner, a calculatedreflected light pattern on the two-dimensional light-receiving element100 when the apparatus arrangement of the specular gloss measuringmethod is adopted can be obtained by the measuring apparatus of thefirst embodiment. In order to output a standard value of JIS Z 8741, alight amount, which enters a light-receiving side area having a width of1.8° and a length of 3.6°, which are defined by an aperture angle, hasto be calculated. However, that light amount can be easily calculatedfrom the calculated reflected light pattern on the two-dimensionallight-receiving element 100.

The measurement of the specular gloss has been explained. However, asfor haze and distinctness-of-image gloss measurements, similarcalculations can be made. As for an image clarity measurement, acomb-tooth slit defined in the JIS K 7374 standard is assumed as alight-receiving area assumed on the two-dimensional light-receivingelement 100. An image clarity can be calculated from maximum and minimumtransmitted light amounts during a moving process of the assumedlight-receiving area by one slit pitch. When a light irradiationdirection in the measuring apparatus is configured to be changed to 20°,45°, 60°, and 85° like in a conventionally manufactured specular glossmeasuring apparatus, evaluation values specified in various standards inassociation with a specular gloss, haze, image clarity, anddistinctness-of-image gloss can be acquired by a single measuringapparatus.

As described above, since the measuring apparatus of the firstembodiment can acquire various reflection characteristics of the surface10, the user need not selectively use a plurality of apparatusesdepending on types of reflection characteristics. Also, since themeasuring apparatus of the first embodiment uses, as the light source 1,a light source having a certain size in place of a point light source,it is effective in terms of S/N, thus allowing measurements within ashort period of time.

Second Embodiment

FIG. 4 shows a schematic arrangement of a measuring apparatus accordingto the second embodiment. Unlike in the first embodiment, a stop 31 hasa rectangular slit in place of a circular aperture. The rectangular slitof the stop 31 has an aperture angle of 0.75° in a widthwise directionand that of 2.5° in a lengthwise direction, which are defined in thestandard required to measure a specular gloss. For this reason, byadding outputs of an element of an aperture angle on the light-receivingdevice side, which is designated by the standard, on a two-dimensionallight-receiving element 100, a specular gloss which matches the standardof a specular gloss measuring method can be easily acquired. Likewise,as for a haze measurement, since the aperture angle on the light sourceside, which is designated by the standard, is the same, a haze can beeasily acquired.

On the other hand, in the same manner as in the process described usingFIG. 3 of the first embodiment, a reflection pattern BRDF 2 of a pointlight source can be calculated or associated by advanced measurementsfrom a BRDF 1A by specular reflected light upon trimming along an AAsection of the two-dimensional light-receiving element 100. Therefore,even when the measuring apparatus of the second embodiment is used, animage clarity can be measured. The measuring apparatus of the secondembodiment requires a smaller calculation volume than that of the firstembodiment, and is further effective in that the apparatus arrangementperfectly matches the standard upon measuring a specular gloss and haze.The measuring apparatus of the second embodiment can cope withmeasurements in only one direction. Hence, a one-dimensionallight-receiving element may be disposed in a direction of AA in place ofthe two-dimensional light-receiving element 100. In this case, since adata amount is greatly reduced, a load on signal processing can bereduced.

Third Embodiment

FIG. 5 shows a schematic arrangement of a measuring apparatus accordingto the third embodiment. Unlike in the first and second embodiments, astop 31 has a hexagonal aperture in place of a circular aperture orrectangular slit. In this case, reflection patterns in three directionsperpendicular to three pairs of sides of a hexagon can be measured. Likein the first and second embodiments, a specular gloss, haze, and imageclarity can be measured. Since the measuring apparatus of the thirdembodiment can measure reflection patterns in two directions differentfrom an AA section, in addition to measurements that match the standardsit can also make determination when a reflection pattern has ananisotropy. In the third embodiment, the stop 31 has a hexagonalaperture, but it may have an n-sided polygonal aperture other than thehexagonal aperture. The n-sided polygon is desirably an even-sidedpolygon (especially, a regular even-sided polygon) in terms of symmetry.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-281756 filed Dec. 25, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A measuring apparatus for measuring a reflection characteristic of a surface, the measuring apparatus including: an illumination device including a first surface light source configured to cause light emitted from the first surface light source to be incident on the surface; a detector, including a light-receiving surface configured to receive light reflected by the surface, configured to detect a first light intensity distribution formed on the light-receiving surface; a memory; and a processor configured to estimate, based on the first light intensity distribution detected by said detector and information stored by said memory, a second light intensity distribution detectable by said detector in a case where said illumination device causes light emitted from a second surface light source, at least one of a shape and a size of which is different from that of the first surface light source, to be incident on the surface, and to obtain the reflection characteristic of the surface based on the estimated second light intensity distribution, wherein the information shows a relation between a plurality of third light intensity distributions detectable by said detector in a case where light emitted from the first surface light source is caused to be incident on a plurality of surfaces having reflection characteristics different from each other and a plurality of fourth light intensity distributions detectable by said detector in a case where light emitted from a point light source set at a position of the first surface light source is caused to be respectively incident on the plurality of surfaces.
 2. The apparatus according to claim 1, wherein said processor is configured to obtain, based on a specular reflected light component and a diffuse reflected light component of the second light intensity distribution and the third light intensity distribution formed on an evaluation area set with respect to the light-receiving surface.
 3. The apparatus according to claim 2, wherein a measuring condition, settable in the apparatus, includes at least one of the shape of the second surface light source, the size of the second surface light source, and the evaluation area of the light-receiving surface.
 4. The apparatus according to claim 1, wherein the second surface light source is a circular light source, and said detector includes a two-dimensional light-receiving element array.
 5. The apparatus according to claim 1, wherein the second surface light source is a rectangular light source, and said detector includes one of a two-dimensional light-receiving element array and a one-dimensional light-receiving element array.
 6. The apparatus according to claim 1, wherein the second surface light source is an n-sided polygonal light source, and said detector includes a two-dimensional light-receiving element array.
 7. The apparatus according to claim 1, wherein the reflection characteristic includes at least one of a specular gloss, a haze, a distinctness-of-image gloss, and an image clarity.
 8. The apparatus according to claim 1, wherein said processor is configured to estimate a specular reflected light component of the second light intensity distribution based on a Gaussian distribution, and to estimate a diffuse reflected light component of the second light intensity distribution based on Lambert scattering.
 9. The apparatus according to claim 8, wherein said processor is configured to estimate the diffuse reflected light component of the second light intensity distribution based on data of a diffuse reflectance of the surface, and data of a light intensity distribution formed on the light-receiving surface with a reference surface having a known diffuse reflectance as a surface to be measured.
 10. The apparatus according to claim 1, wherein said processor is configured to estimate, based on the first light intensity distribution, the second light intensity distribution formed on the light-receiving surface by reflected light from the surface in a case where a point light source is disposed at a position of the second surface light source, and to obtain a specular reflected light component and a diffuse reflected light component of the second light intensity distribution by dividing the estimated second light intensity distribution.
 11. The apparatus according to claim 1, wherein said processor is configured to divide the first light intensity distribution into a specular reflected light intensity distribution and a diffuse reflected component of the first light intensity distribution, and to estimate a specular reflected light component and a diffuse reflected light component of the second light intensity distribution respectively based on the two components obtained by the division.
 12. The apparatus according to claim 11, wherein said processor is configured to estimate the diffuse reflected light component of the second light intensity distribution based on the diffuse reflected light component of the first light intensity distribution, and a ratio between a size of the point light source and a size of the second surface light source.
 13. The apparatus according to claim 11, wherein said processor is configured to estimate the specular reflected light component of the second light intensity distribution based on information indicating a relation between the specular reflected light component of the first light intensity distribution and the specular reflected light component of the second light intensity distribution, and the specular reflected light component of the first intensity distribution.
 14. The apparatus according to claim 1, wherein the reflected light includes a specular reflected light and a diffuse reflected light, and said processor is configured to estimate the second light intensity distribution by dividing the first light intensity distribution into a specular reflected light component and a diffuse reflected light component.
 15. A method of measuring a reflection characteristic of a surface, the method comprising: causing light emitted from a first surface light source to be incident on the surface and receiving light reflected by the surface to detect a first light intensity distribution formed on a light-receiving surface; and characterized by estimating, based on the first light intensity distribution and information, a second light intensity distribution detectable in a case where light emitted from a second surface light source, at least one of a shape and a size of which is different from that of the first surface light source, is caused to be incident on the surface; and obtaining the reflection characteristic of the surface based on the estimated second light intensity distribution, wherein the information shows a relation between a plurality of third light intensity distributions detectable in a case where light emitted from the first surface light source is caused to be incident on a plurality of surfaces having reflection characteristics different from each other and a plurality of fourth light intensity distributions detectable in a case where light emitted from a point light source set at a position of the first surface light source is caused to be respectively incident on the plurality of surfaces.
 16. A measuring apparatus for measuring a reflection characteristic of a surface, the apparatus comprising: an illumination device including a first surface light source, and configured to cause light emitted from the first surface light source to be incident on the surface; a detector configured to receive light reflected by the surface, and to detect a first light intensity distribution formed on the detector; a memory; and a processor configured to estimate, based on the first light intensity distribution detected by the detector and information stored by the memory, a second light intensity distribution to be formed on the detector by reflected light from the surface and to be detected by the detector in a case where a second surface light source, at least one of a shape and a size of which is different from that of the first surface light source, is arranged instead of the first surface light source, and to obtain the reflection characteristic of the surface based on the estimated second light intensity distribution, wherein the information includes information for estimating, based on the first light intensity distribution, a light intensity distribution to be formed on the detector by reflected light from the surface and to be detected by the detector in a case where a point light source is arranged instead of the first surface light source.
 17. A method of measuring a reflection characteristic of a surface, the method comprising: causing light emitted from a first surface light source to be incident on the surface and receiving light reflected by the surface to detect a first light intensity distribution formed on a detector; estimating, based on the first light intensity distribution and information, a second light intensity distribution to be formed on the detector by reflected light from the surface and to be detected by the detector in a case where a second surface light source, at least one of a shape and a size of which is different from that of the first surface light source, is arranged instead of the first surface light source; and obtaining the reflection characteristic of the surface based on the estimated second light intensity distribution, wherein the information includes information for estimating, based on the first light intensity distribution, a light intensity distribution to be formed on the detector by reflected light from the surface and to be detected by the detector in a case where a point light source is arranged instead of the first surface light source. 